1. Technical Field
This invention relates to a method for manufacturing composite molded articles and to the articles obtained therefrom. In further detail, this invention pertains to a method for manufacturing a composite molded article comprising a surface film of superior weather-resistance integrally molded on a surface of a polynorbornene base material. The method is achieved via an in-mold coating process in combination with a reaction injection molding (RIM) process.
2. State of the Art
Polynorbornene derived molded articles obtained by bulk polymerization of norbornene monomers in a mold by RIM have recently received wide attention. However, painting and coating of such articles are necessary, particularly when these molded articles are used outdoors, because of their insufficient weathering properties.
However, in order to improve the surface of polynorbornene molded articles by painting, the article has to be thoroughly rinsed with solvent and warm water to remove the mold releasing agent and soil from handling, etc., that have deposited on the surface. The article is then submitted to a primer treatment and/or a paint treatment, etc. Consequently, the processes are complex and the procedure is difficult. Moreover, molded articles obtained by RIM generally present problems in that pin holes readily form in the paint film.
Polynorbornene polymers are usually yellow or brown in appearance. Even when they are colored by adding dyes, changes in color readily develop over time. Attempts have been made to improve the surface conditions of molded articles by lamination of colored sheets and printed sheets made from plastic, but adhesion with the norbornene polymer is often very poor. Therefore, a composite material for practical use has yet to be obtained.
Consequently, the present inventors filed a patent application (Application No. Sho 63(1988)-171038) for a composite material of a layer that is made from an olefinic polymer and/or hydrocarbon thermoplastic elastomer on a base that is made from a polynorbornene polymer. This composite material has superior properties in that it has good interface adhesion, the surface layer can be of any color, and it has improved weather resistance.
This composite material is manufactured by feeding a bulk polymerizable a reaction mixture containing a norbornene monomer and metathesis catalyst in a mold having a layerforming material made of an olefinic polymer on its inside surface. However, manufacture of molded articles of complex shapes and deep draw is difficult. In addition, surface-molding materials with good interface adhesion are limited.
On the other hand, the so-called in-mold coating method is well known as a method for painting thick RIM molded articles (Patent No. Sho 63(1988)-45291, Japanese Kokai Patent No. Sho 59(1984)-224328, etc.). By utilizing this method, many process steps are necessary. For instance, a releasing agent is applied to the inside of the mold, a urethane undercoat is then applied and dried, a urethane RIM material (reaction solution) is injected into the mold and reaction injection molding is performed so that the undercoat paint film is transferred onto the molded article. The paint film is hardened by post-curing after removal from the mold, the releasing agent is rinsed and removed from the paint film, and then another undercoat and a topcoat are applied. In another method, RIM material is injected and molded and then paint is injected into the mold under high pressure. However, special molds and facilities are needed.
Painted molded articles that are obtained by inmold coating have yet to be manufactured using RIM with norbornene monomers. The reason for this is that there is a chance that the paint will impair the polymerization of the norbornene monomer, adhesion between polynorbornene polymer and paint film is insufficient, and there are no paint film materials that transfer to the surface of the molded article.